Real-time estimation of human core body temperature based on non-invasive physiological measurements

ABSTRACT

An embodiment of the invention provides a method of estimating a body temperature of an individual where physiological data is received from at least one sensor  510 . Environmental data is received and the physiological data and the environmental data are input into a model. The model generates an estimated body temperature and an estimated physiological condition based on the physiological data and the environmental data. A processor  520  compares the estimated physiological condition to a measured physiological condition in the physiological data. A controller  530  modifies at least one parameter in the model when the difference between the estimated physiological condition and the measured physiological condition is above a threshold.

This patent application is the National Stage Entry of International Application No. PCT/US2017/047547, filed on Aug. 18, 2017, which claimed the benefit of and priority to U.S. Patent Application No. 62/379,522 filed on Aug. 25, 2016 in the U.S. Patent and Trademark Office, which are hereby incorporated by reference in its entirety.

I. FIELD OF INVENTION

The present invention relates to systems, methods, and computer program products for real-time estimation of human core body temperature based on non-invasive physiological measurements. Heat injury is a problem for the U.S. Armed Forces, especially during deployments to localities with hot and humid climates, and trends show the number of heat injury cases to be on the rise each year. From 2006 through 2010, there were 2887 heat injuries across the services, including 311 cases of heat stroke. Nevertheless, to date, there are no practical solutions to alert service members of an impending heat injury and help prevent them.

II. SUMMARY OF THE INVENTION

An embodiment of the invention provides a method of estimating a body temperature of an individual where physiological data is received from at least one sensor. Environmental data is received and the physiological data and the environmental data are input into a model. The model generates an estimated body temperature and an estimated physiological condition based on the physiological data and the environmental data. A processor compares the estimated physiological condition to a measured physiological condition in the physiological data. A controller modifies at least one parameter in the model when the difference between the estimated physiological condition and the measured physiological condition is above a threshold.

III. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.

FIG. 1 illustrates a system for real-time individualized core body temperature estimation according to an embodiment of the invention.

FIGS. 2A-2D are graphs illustrating the performance of the individualized core body temperature model according to an embodiment of the invention.

FIG. 3 are graphs illustrating core temperature predictions according to an embodiment of the invention.

FIG. 4 is a block diagram illustrating a method for estimating a body temperature of an individual according to an embodiment of the invention.

FIG. 5 is a flow diagram illustrating the initialization and subsequent steps of the Kalman filter algorithm for real-time core body temperature estimation according to an embodiment of the invention.

FIG. 6 illustrates a system for estimating a body temperature of an individual according to an embodiment of the invention.

FIG. 7 illustrates a computer program product for estimating a body temperature of an individual according to an embodiment of the invention.

IV. DETAILED DESCRIPTION

Non-limiting embodiments of the present invention are discussed in detail below. While specific configurations are discussed to provide a clear understanding, it should be understood that the disclosed configurations are provided for illustration purposes only. A person of ordinary skill in the art will recognize that other configurations may be used without departing from the spirit and scope of the invention.

At least one embodiment of the invention provides a system that determines an individual's core body temperature based on noninvasive measurements of the individual's heart rate, activity, and skin temperature, as well as measurements of two environmental variables, such as ambient temperature and relative humidity. A fitness-tracking device, such as an electronic wristband or watch, can collect the individual's non-invasive physiological data and wirelessly transmit the data to a mobile computing platform (e.g., smartphone, tablet computer). In at least one embodiment, the mobile computing platform is on the fitness-tracking device.

As illustrated in FIG. 1 , physiological data can be captured by a fitness-tracking device 110 and input into an estimation model in a mobile computing platform 120, where the estimation model can use the physiological data to adapt the model parameters to the individual and provides individualized core body temperature estimates in real time. In at least one embodiment, the fitness-tracking device 110 includes a chest strap or a wrist watch, which continually collects an individual's heart rate, activity (e.g., via a 3 axis accelerometer), and skin temperature.

FIG. 1 illustrates a schematic representation of a system for real-time individualized core body temperature estimation. Data can include the measured heart rate (HR), skin temperature (TS), and activity (AC) from a wrist-worn fitness-tracking and measurements of two environmental variables (e.g., ambient temperature (TA) and relative humidity (RH)) can be wirelessly transmitted to the mobile computing platform. The activity (accelerometer) data and environmental factors can drive the mathematical model, while HR and TS data can be used to improve the quality of the core body temperature (TC) estimates via a Kalman filter algorithm. This process can be repeated every minute (or at another sampling rate) after each measurement of HR, AC, and TS.

The core body temperature estimation mathematical model can include a physiological mathematical model and a Kalman filter algorithm. These two elements can feed information to one another to “learn” the individual's response to environmental and exertional heat stresses, and produce an individualized estimation of core body temperature in real time (FIG. 1 ). The mathematical model can describe the heat balance between the body core and the external environment in terms of three equations that relate physical activity to heart rate, heart rate to core body temperature, and core body temperature to skin temperature. First, the mathematical model can use the current activity level of the subject, as measured by an accelerometer, and hourly (or another frequency) measurements of ambient temperature and relative humidity to estimate the heart rate, skin temperature, and core body temperature of the subject.

In at least one embodiment, the Kalman filter considers the errors between the estimates provided by the mathematical model and the actual measured heart rate and skin temperature of the individual, and can provide corrections by adjusting up to seven parameters in the mathematical model. In at least one embodiment, the seven parameters, which may be continually adjusted and updated, account for features such as the rate of heat gain due to metabolic activity, the rate of convective heat loss or gain from the skin surface to the environment, and the rate of heat loss to the environment due to sweat evaporation, among others. The algorithm can repeat this procedure after measurements of heart rate, activity, and skin temperature every minute to update the model parameters, individualize the model, and provide new estimates of core body temperature that reflect the subject's physiological response to environmental and exertional heat stress.

FIGS. 2A-2D show the performance of the individualized core body temperature model. Specifically, FIGS. 2A-2D illustrate the model-estimated and measured (via an ingestible pill) core body temperature for two subjects whose temperature exceeded 39° C. FIGS. 2A-2D also show the correlation (r) between the measured and estimated core body temperatures for the corresponding subjects (r ranged from 0.90 to 0.92). FIGS. 2A-2B illustrate the core body temperatures of two study subjects over 12 hours of activity as measured by a thermometer radio pill (dashed lines) and estimated by the individualized model (solid lines). FIGS. 2C-2D show the correlation between measured and model-estimated core body temperatures for both subjects (RMSE=root mean squared error).

In contrast to an invasive, ingestible thermometer pill, which does not offer a practical means to continually monitor a large number of individuals, the system is based on non-invasive physiological measurements, which may be available through use of a range of fitness-tracking devices. Furthermore, unlike data-driven mathematical algorithms that may not capture an individual's underlying physiology and may only provide the response of an average individual, the system can implicitly account for subject-specific variations in thermoregulatory responses. This can provide core body temperature estimates that are individualized to the specific person. This ability to continually learn an individual's response to heat stress can allow for a more accurate and broader applicability of the model. In addition, because the model can rely on multiple physiological measurements, it is less susceptible to the failure of any one sensor. For instance, if the accelerometer fails, the model can still rely on heart rate and skin temperature measurements.

In at least one embodiment, the system can also be used to predict core body temperature (e.g., 20 minutes in advance) and provide ample time to intervene and prevent an impending heat injury. This can be achieved by coupling a series of estimated core body temperatures with a predictive model in the development of a real-time, heat-injury warning system.

Core body temperature can be predicted using an autoregressive (AR) model. Given core body temperature values y_(n−i) estimated, for example, every 1 minute, where n is the current discrete time index and i=0, 1, . . . , m−1, an AR model of order m can predict temperature ŷ_(n+1), at time point n+1, through a linear combination of the antecedent core temperature estimates as follows:

${\overset{\frown}{y}}_{n + 1} = {\sum\limits_{i = 0}^{m - 1}{b_{i}y_{n - 1}}}$ where b denotes the vector of m AR coefficients. In at least one embodiment, it is assumed that activity, heart rate, and skin temperature stay the same. To make predictions M time steps ahead, one can iteratively use the above equation M times, substituting the unobserved temperatures at n≥n+1 in the summation by their corresponding predicted values. The order m of the model can specify the required initial waiting period for which temperature values need to be estimated before real-time predictions can be made. FIG. 3 shows 20-minute-ahead predictions for the same two subjects illustrated in FIG. 2 . In addition to the predictions, FIG. 3 also shows the measured and estimated core temperature values.

At least one embodiment of the invention provides a system and method for real-time, non-invasive estimation of core body temperature using an estimation model based on phenomenological and conservation of energy principles. The system can continually adapt the estimation model to an individual based on the individual's non-invasive physiological measurements. The system can automatically account for individual-specific variations in thermoregulatory responses due to acclimation and reactions to exogenous factors, such as clothing and environmental conditions.

FIG. 4 illustrating a method for estimating a body temperature of an individual according to an embodiment of the invention (e.g., using the system 400). A processor can receive physiological data from a sensor in a wearable measuring device (a wearable accelerometer) 410. The processor can be in the wearable measuring device or in wireless communication with the wearable measuring device. The physiological data can include the heart rate, the skin temperature, and/or activity data of the individual. The physiological data can be from different body locations. The activity data can include the running speed of the individual and/or an activity score of the individual (e.g., low, moderate, high, and very high). In at least one embodiment, the processor receives the 3-D body acceleration of the individual from the wearable measuring device and maps the body acceleration into Metabolic Equivalent (MET, amount of energy burned during exercise) units to determine the activity score of the individual.

The processor can also receive environmental data (ambient temperature and/or humidity) from one or more additional sensors in the wearable measuring device and/or an online resource (e.g., weather website) 420. In at least one embodiment, the processor determines the location of the sensor with a global positioning system (GPS) device in the measuring device and queries an online resource with the location of the sensor to retrieve the environmental data.

The processor uses the received physiological data and the environmental data a model, and the model generates an estimated core body temperature and an estimated physiological condition (e.g., heart rate and/or skin temperature) based on the physiological data and the environmental data 430. In at least one embodiment, the physiological data and/or the environmental data are constantly measured such that the estimating of the core body temperature of the individual is performed in real time. The model can include a physiological mathematical model and a Kalman filter that feed information to one another to learn the individual's response to environmental and exertional heat stresses.

More specifically, the physiological mathematical model can include a first equation that relates physical activity to heart rate, a second equation that relates heart rate to core body temperature, and a third equation that relates core body temperature to skin temperature. The first mathematical equation above can be motivated by the observation that an increase in physical activity A_(C) leads to a rapid increase in heart rate H_(R), followed by an exponential decay when A_(C) decreases. In at least one embodiment, this is mathematically represented by:

$\frac{d\Delta H_{R}}{dt} = {{{- \alpha_{1}}\Delta H_{R}} + {\beta A_{C}^{4}}}$

where ΔH_(R) denotes the change in heart rate from a resting state H_(R0) (i.e., ΔH_(R)=H_(R)−H_(R0)), α₁ denotes the rate constant for H_(R), and β represents the gain in H_(R) due to physical activity. In at least one embodiment, A_(C) ⁴ is used to ensure good separation of the H_(R) due to different activity levels; a feature noted during data analysis, e.g., A_(C)=2 (moderate activity) must lead to a larger increase in H_(R) when compared to A_(C)=1 (light activity). H_(R0) can be set as the mean of the measured H_(R) for the initial 5 minutes of the data (˜80 beats/min) representing light activity levels.

In at least one embodiment of the invention, the second and third equations in the model represent the core temperature T_(C) and skin temperature T_(S), respectively, at the current time, as:

${\frac{d\Delta T_{C}}{dt} = {{{- \alpha_{2}}\Delta T_{C}} + {\gamma_{1}\Delta H_{R}} - {\gamma_{2}\left( {T_{C} - T_{S}} \right)}}}{\frac{d\Delta T_{S}}{dt} = {{- {\alpha_{3}\left( {T_{S} - T_{A}} \right)}} - {\alpha_{4}\left( {P_{S} - P_{A}} \right)} + {\gamma_{2}\left( {T_{C} - T_{S}} \right)}}}$ where ΔT_(C)=T_(C)−T_(C0) and ΔT_(S)=T_(S)−T_(S0), with T_(C0) and T_(S0) denoting the initial core and skin temperatures, respectively, P_(S) denotes the vapor pressure of water for T_(S), and P_(A) represents the vapor pressure of water due to the heat index perceived by humans at a given ambient temperature T_(A) and relative humidity R_(H). T_(S0) can be set as the mean of the measured T_(S) during the initial 5 minutes and T_(C0) to 37° C. In the second equation of the model, α₂ can denote the thermoregulatory rate constant of T_(C), γ₁ can denote the rate of heat gain due to metabolic activity (H_(R)), and γ₂ can represent the rate of heat loss/gain from the core to the skin. In the third equation of the model, α₃ can denote the rate of convective heat loss/gain from the skin to the environment and α₄ can denote the rate of heat loss to the environment due to sweat evaporation. Thus, the mathematical model consists of three states (ΔH_(R), ΔT_(C), and ΔT_(S) corresponding to the three equations of the model) and seven unknown parameters (α₁, α₂, β, γ₁, γ₂, α₃, and α₄).

The processor can compare the estimated physiological condition to a measured physiological condition in the physiological data 440. For example, the estimated physiological condition includes an estimated heart rate and an estimated skin temperature; and the measured physiological condition includes a measured heart rate and a measured skin temperature. The measured heart rate and the measured skin temperature can be used to customize the model to the individual via a Kalman filter algorithm.

A controller connected to the processor can modify one or more parameters in the model when the difference between the estimated physiological condition and the measured physiological condition is above a threshold 450. The modifying of the parameter(s) in the model can include modifying a rate constant for the heart rate signal (α₁), a thermoregulatory rate constant for the core temperature signal (α₂), a rate of convective heat loss/gain from the skin to the environment (α₃), a rate of heat loss to the environment due to sweat evaporation (α₄), a gain in heart rate due to physical activity (β), a rate of heat gain due to metabolic activity (γ₁), and/or a rate of heat loss/gain from the core to the skin (γ₂).

The model can use the physiological data and the environmental data to learn a physiological response of the individual and automatically adjust parameter(s) in the model to produce an individualized model. The model can include a Kalman filter where the comparing of the estimated physiological condition to the measured physiological condition and the modifying of the at least one parameter in the model is performed by the Kalman filter. In at least one embodiment, a communications device such as a transmitter or a transceiver connected to the sensor sends data from the sensor to an external computing device (e.g., smartphone, tablet computer), where the processor and the controller are on the external computing device. The processor can predict a future core body temperature of the individual based on the estimated core body temperature and at least one additional estimated core body temperature, where the estimated core body temperature(s) are generated after the parameter(s) in the model are modified.

FIG. 5 is a flow diagram illustrating the initialization and subsequent steps of the Kalman filter algorithm for real-time core body temperature (T_(C)) estimation. The algorithm can be initialized with θ, σ_(θ) ², the H_(R) and T_(S) measurement noise variances (matrix R), and the process noise variance σ² estimated from the first 10 minutes of data for each subject. After initialization, the algorithm can use u_(k+1) to drive the mathematical model to estimate H_(R) and T_(S) (Estimation step). Then, by scaling the error e_(k+1) between the filtered measurements and the model-estimated H_(R) and T_(S) by the Kalman gain K_(k+1), the algorithm can update the model parameters and the T_(C) estimates at each time index (Update step) until the end of the measured time-series data.

To implement the Kalman filter algorithm, the continuous-time nonlinear model (i.e., the three previous equations) can be converted into a discrete linear model. In at least one embodiment, to discretize the model, the three equations are of the form {dot over (x)}=f(x, u), with states x=[ΔH_(R) ΔT_(C) ΔT_(S)θ]^(T), where θ=ϕ^(1/2) (to ensure non-negative parameter values), with ϕ representing the vector of the six adjustable model parameters, f(⋅) denoting a set of nonlinear functions, and u=[A_(C) ⁴ T_(A) P_(A)]^(T). Subsequent steps can include computing the Jacobian of f(x, u) [1] and discretizing the results to obtain a linear time-varying model [2]. In at least one embodiment, the discrete model has state equations x_(k+1)=F_(k)x_(k) G_(k) u_(k+1) and output equations y_(k)=C x_(k)+y₀, where F_(k) and G_(k) denote the discrete linearized state-transition and input matrices, respectively, obtained at each time index k, C denotes the matrix that outputs the estimated ΔH_(R) and ΔT_(S) signals, and y₀=[H_(R0) T_(S0)]^(T) represents the vector of the mean values of H_(R) and T_(S) from the initial 10 minutes of data, which are used to initialize the model.

The flowchart in FIG. 5 depicts the initialization of, and sequence of steps involved in, the Kalman filter algorithm according to an embodiment of the invention. In at least one embodiment, the algorithm is initialized with parameter values (θ) obtained from previously published studies, as described above (represented in the initial state vector x₀), their corresponding variances σ_(θ) ² (represented in the initial state-error covariance matrix P₀), the noise variances of the H_(R) and T_(S) measurements obtained from the first 10 minutes of data (represented in matrix R), and a measure of the systemic uncertainty (σ² in matrix Q) between the mathematical model estimates and a subject's data. Using each subject's first 10 minutes of data, σ² can be estimated by first filtering the measured H_(R) and T_(S) in real time, using a second-order, causal low-pass Butterworth filter with a cut-off frequency of 3.3 mHz, to reject noise while preserving the frequency band that overlaps with the measured T_(C). A 5-minute moving average of the measured A_(C), the measured T_(A), and P_(A) (computed from the measured T_(A) and R_(H)) can be used to drive the mathematical model. The error between the filtered H_(R) and T_(S) data and the corresponding model estimates can be computed, which can be linearly related to the systemic uncertainty in the model states. This can allow the estimation of σ² by solving the resulting linear least-squares problem [3].

After initialization, the Kalman filter algorithm can proceed in the following manner: at each 15-s discrete time interval, the algorithm can use a 5-minute moving average of the measured (or computed) A_(C), the measured T_(A), the P_(A) at the present time index k+1, and the model parameters obtained up to time index k to estimate the model states x_(k+1|k) (FIG. 5 , Estimation step). In the estimation step, the algorithm can also estimate the state-error covariance matrix P_(k+1|k), using the model parameters up to time index k and the process noise matrix Q. Subsequently, the algorithm can compute the Kalman gain K_(k+1) and use the error e_(k+1) between the filtered measurements (y_(k+1)) and the estimated H_(R) and T_(S) (Cx_(k+1|k)) to update the T_(C) estimate (an element of the state vector x_(k+1|k+1)), the model parameters, and the state-error covariance matrix P_(k+1|k+1) (FIG. 5 , Update step). In situations where H_(R) or T_(S) measurements were temporarily unavailable (i.e., missing measurements), it can be assumed that the noise characteristics of the error at time point k+1 would not be drastically different from the previous time point k, and hence set e_(k+1) to e_(k) in the Update step. The algorithm can repeat this procedure for each time step until the end of the time-series data.

FIG. 6 illustrates a system 600 for estimating a body temperature of an individual according to an embodiment of the invention. A sensor(s) 610 in a measurement device can be configured to measure physiological data of the individual (e.g., heart rate, skin temperature, activity data). For example, the physiological data includes activity data including running speed of the individual in miles per hour as detected by GPS or a pedometer. In another example, the physiological data includes an activity score of the individual (e.g., low, moderate, high, and very high), which is calculated by a processor using data obtained by heart rate monitor, GPS, pedometer, piezoelectric sensor, or other sensor on the individual. The activity score can also be manually input into the system by the individual, medical professional, or other user.

A processor 620 can receive the measured physiological data from the sensor(s) 610 and environmental data (e.g., ambient temperature, humidity) from an online resource. In at least one embodiment, the system 600 includes a second sensor in the measurement device to measure the environmental data instead of retrieving information from a data source such as an online resource. In another embodiment, the system 600 includes or is in communication with a GPS device in the measurement device to determine the location of the sensor 610, where the processor 620 queries an online resource with the location of the sensor to retrieve the environmental data. As used herein the term “processor” includes a computer hardware device connected to the sensor 610, such as, for example, a CPU, integrated circuit, or microprocessor. As used herein, the term “connected” includes operationally connected, logically connected, in communication with, physically or wirelessly connected, engaged, coupled, contacts, linked, affixed, and attached.

The processor 620 can input the physiological data and the environmental data into a model; and the model can generate an estimated core body temperature and an estimated physiological condition based on the physiological data and the environmental data. As discussed more fully above, the model includes a physiological mathematical model having a first equation that relates physical activity to heart rate, a second equation that relates heart rate to core body temperature, and a third equation that relates core body temperature to skin temperature.

The processor 620 can compare the estimated physiological condition (e.g., estimated heart rate, estimated skin temperature) to a measured physiological condition in the physiological data (e.g., measured heart rate, measured skin temperature). The model can use the physiological data and the environmental data to learn a physiological response of the individual and automatically adjusts the at least one parameter in the model to produce an individualized model.

More specifically, a controller 630 can modify one or more parameters in the model when the difference between the estimated physiological condition and the measured physiological condition is above a threshold. As used herein the term “controller” includes a computer hardware device connected to the processor 620, such as, for example, a CPU, integrated circuit, or microprocessor. The controller 630 can modify a rate constant for the heart rate signal (α₁), a thermoregulatory rate constant for the core temperature signal (α₂), a rate of convective heat loss/gain from the skin to the environment (α₃), a rate of heat loss to the environment due to sweat evaporation (α₄), a gain in heart rate due to physical activity (β), a rate of heat gain due to metabolic activity (γ₁), and/or a rate of heat loss/gain from the core to the skin (γ₂).

The present invention may be a system, a method, and/or a computer program product at any possible technical detail level of integration. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention.

The computer readable storage medium is a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of the computer readable storage medium includes the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or raised structures in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire.

Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network. The network may comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and/or edge servers. A network adapter card or network interface in each computing/processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing/processing device.

Computer readable program instructions for carrying out operations of the present invention may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, configuration data for integrated circuitry, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++, or the like, and procedural programming languages, such as the “C” programming language or similar programming languages. The computer readable program instructions may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions.

These computer readable program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function/act specified in the flowchart and/or block diagram block or blocks.

The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other device implement the functions/acts specified in the flowchart and/or block diagram block or blocks.

The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the blocks may occur out of the order noted in the Figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.

Referring now to FIG. 7 , a representative hardware environment for practicing at least one embodiment of the invention is depicted. This schematic drawing illustrates a hardware configuration of an information handling/computer system in accordance with at least one embodiment of the invention. The system comprises at least one processor or central processing unit (CPU) 10. The CPUs 10 are interconnected with system bus 12 to various devices such as a random access memory (RAM) 14, read-only memory (ROM) 16, and an input/output (I/O) adapter 18. The I/O adapter 18 can connect to peripheral devices, such as disk units 11 and tape drives 13, or other program storage devices that are readable by the system. The system can read the inventive instructions on the program storage devices and follow these instructions to execute the methodology of at least one embodiment of the invention. The system further includes a user interface adapter 19 that connects a keyboard 15, mouse 17, speaker 24, microphone 22, and/or other user interface devices such as a touch screen device (not shown) to the bus 12 to gather user input. Additionally, a communication adapter 20 connects the bus 12 to a data processing network 25, and a display adapter 21 connects the bus 12 to a display device 23 which may be embodied as an output device such as a monitor, printer, or transmitter, for example.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the root terms “include” and/or “have”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of at least one other feature, integer, step, operation, element, component, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of all means plus function elements in the claims below are intended to include any structure, or material, for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

INDUSTRIAL APPLICABILITY

A system and method of estimating a body temperature of an individual is provided. The provided systems and methods are particularly suited for receiving environmental and physiological data from a sensor, and inputting the data into a model, where the model generates an estimated body temperature and an estimated physiological condition based on the data. The estimated physiological condition is compared to a measured physiological condition in the physiological data. One or more parameters in the model are modified when the difference between the estimated physiological condition and the measured physiological condition is above a threshold.

REFERENCES

-   [1] Ozaki T. The local linearization filter with application to     nonlinear system identifications. Proc first US/Japan Conf Frontiers     Stat Modeling: An Informational Approach, Springer, p. 217-240,     1994. -   [2] Chen C-T. Linear System Theory and Design. 3^(rd) ed. Oxford,     N.Y.: Oxford University Press, 1999. -   [3] Bulut Y, Vines-Cavanaugh D, Bernal D. Process and measurement     noise estimation for Kalman filtering. Structural Dynamics, Conf     Proc Soc Exp Mech Series 3: 375-386, 2011. 

What is claimed is:
 1. A method of estimating a body temperature of an individual and continual customization of a model for estimating the body temperature during performance of the method, said method comprising: receiving with a processor a heart rate of the individual, a skin temperature of the individual, and activity data of the individual from at least one sensor; receiving with the processor an ambient temperature and a humidity; inputting the received activity data of the individual, the received ambient temperature, and the received humidity into the model operating on the processor and the model including a Kalman filter and a physiological model, wherein the physiological model generates an estimated heart rate based on the received activity data and an estimated skin temperature based on a skin temperature vapor pressure and a vapor pressure for a heat index for the received ambient temperature and the received humidity to account for a heat transfer from a skin of the individual to an environment in which the individual is present; modifying by a controller using the Kalman filter at least one parameter in the physiological model based on a first error between the estimated heart rate and the received heart rate and/or a second error between the estimated skin temperature and the received skin temperature; and estimating with the physiological model the body temperature reflecting a heat balance of the individual where the physiological model uses the at least one parameter that has been modified by the Kalman filter, and wherein modifying at least one parameter customizes the physiological model to the individual by adapting to continual physiological changes in the individual.
 2. The method according to claim 1, further comprising: receiving a 3-D body acceleration of the individual from a wearable measuring device; mapping the 3-D body acceleration into metabolic equivalent units to determine an activity score of the individual where the activity data includes the activity score.
 3. The method according to claim 1, wherein the physiological model uses the following parameters: a rate constant for heart rate; a thermoregulatory rate constant; a rate of convective heat loss/gain from a skin compartment to the environment; a rate of heat loss to the environment due to sweat evaporation; a rate of heat gain due to metabolic activity; and a rate of heat loss/gain from the body temperature to the skin compartment.
 4. The method according to claim 1, wherein the physiological mathematical model and the Kalman filter feed information to one another to learn a response for the individual to environmental and exertional heat stresses.
 5. The method according to claim 1, wherein said receiving of the ambient temperature and the humidity includes: determining a location of the sensor with a global positioning system (GPS) device; and querying an online resource with the location of the sensor to retrieve the ambient temperature and the humidity.
 6. The method according to claim 1, further comprising sending data from the at least one sensor to an external computing device, wherein the processor and the controller are on the external computing device.
 7. The method according to claim 1, further comprising predicting a future body temperature of the individual using an autoregressive model based on the estimated body temperature and at least one additional estimated body temperature, the at least one estimated body temperature being generated after said modifying of at least one parameter in the model.
 8. The method according to claim 1, wherein estimating the body temperature with the physiological model uses the estimated heart rate and the estimated skin temperature; and receiving the heart rate, the skin temperature, activity data, the ambient temperature, and the humidity; inputting; comparing; modifying; and estimating are repeated at predetermined intervals.
 9. The method according to claim 1, wherein the Kalman filter modifies at least one parameter to reduce the first error and/or the second error when estimating a future heart rate and/or a future skin temperature.
 10. A system for estimating a body temperature of an individual, said system comprising: at least one physiological sensor configured to measure physiological data including physical activity, a heart rate, and a skin temperature; at least one environmental sensor configured to measure environmental data; a processor connected to said at least one physiological sensor and said at least one environmental sensor, said processor inputs the physiological data and the environmental data into a model configured to operate on said processor, wherein the model generates two estimated physiological conditions based on the physical activity and/or the environmental data, said processor compares at least one of the estimated physiological conditions to the respective measured physiological condition in the physiological data to find at least one error; and a controller in communication with said processor, said controller modifies at least one parameter in the model with a Kalman filter included in the model based on the at least one error to minimize the at least one error in a future estimation of that at least one physiological condition, and wherein the model further includes a physiological mathematical model using a plurality of parameters in: a first equation that relates the physical activity to an estimated heart rate as one of the estimated physiological conditions using a rate constant for heart rate and a gain heart rate due to the physical activity, a second equation that relates the heart rate to an estimated body temperature using a thermoregulatory rate constant, a rate of heat gain due to metabolic activity with the estimated heart rate, a rate of heat loss/gain from core to skin with a first temperature gradient, and a third equation that relates the body temperature to an estimated skin temperature as another estimated physiological condition using a rate of convective heat loss/gain from the skin to the environment with a second temperature gradient, a rate of heat loss to the environment due to sweat evaporation, and the rate of heat loss/gain from the core to the skin with the first temperature gradient; and wherein said processor is configured to produce the estimated body temperature after the controller modifies at least one parameter in the physiological mathematical model using the second equation.
 11. The system according to claim 10, wherein the model uses the physiological data and the environmental data to learn a physiological response of the individual and automatically adjusts with the Kalman filter the at least one parameter in the physiological mathematical model to produce an individualized model.
 12. The system according to claim 10, wherein the physical activity data of the individual includes an activity score of the individual, said at least one sensor includes a third sensor, said third sensor configured to measure a 3-D body acceleration of the individual, wherein said processor is configured to map the 3-D body acceleration into metabolic equivalent units to determine the activity score of the individual.
 13. The system according to claim 10, wherein the measured heart rate and the measured skin temperature are used to customize the model to the individual based on an output of the Kalman filter.
 14. The system according to claim 10, wherein the physiological mathematical model parameters include: the thermoregulatory rate constant; the rate of convective heat loss/gain; the rate of heat loss to an environment due to sweat evaporation; the gain in heart rate due to physical activity; the rate of heat gain due to metabolic activity; and the rate of heat loss/gain from the estimated body temperature to the skin compartment, and wherein the model parameters are internal to the model and are distinct from the measured physiological data and the measured environmental data that are inputted into the model.
 15. The system according to claim 10, wherein the model includes the physiological mathematical model and the Kalman filter that feed information to one another to learn a response for the individual to environmental and exertional heat stresses.
 16. The system according to claim 10, further comprising a communications device connected to said at least one physiological sensor, said communications device configured to send data from said at least one physiological sensor and said at least one environmental sensor to an external computing device, wherein said processor and said controller are on said external computing device.
 17. The system according to claim 10, wherein said processor is configured to predict with an autoregressive model a future body temperature of the individual based on the estimated body temperature and at least one additional estimated body temperature, the at least one estimated body temperature being generated after said controller modifies of at least one parameter in the model.
 18. A method of estimating a body temperature of an individual, said method comprising: receiving physiological data from at least one sensor, the physiological data including at least one of a heart rate of the individual, a skin temperature of the individual, and activity data of the individual, wherein the activity data of the individual includes at least one of a running speed of the individual and an activity score of the individual; receiving environmental data, the environmental data including at least one of ambient temperature and humidity; inputting the physiological data and the environmental data into a model, wherein the model generates an estimated body temperature and an estimated physiological condition based on the physiological data and the environmental data, wherein the model includes a physiological mathematical model including at least one of: a first equation that relates physical activity to heart rate, wherein the first equation includes: $\frac{d\Delta H_{R}}{dt} = {{{- \alpha_{1}}\Delta H_{R}} + {\beta A_{C}^{4}}}$ where ΔH_(R) represents a change in heart rate from an initial heart rate H_(R0), H_(R) represents a current heart rate, dt represents a change in time, α₁ represents a rate constant for H_(R), β represents a gain in heart rate due to physical activity, and A_(C) represents an activity level, a second equation that relates heart rate to core body temperature, and a third equation that relates core body temperature to skin temperature; comparing by a processor the estimated physiological condition to a measured physiological condition in the physiological data to find a difference; and modifying by a controller at least one parameter in the model when the difference between the estimated physiological condition and the measured physiological condition is above a threshold.
 19. The method according to claim 18, wherein the second equation includes: $\frac{d\Delta T_{C}}{dt} = {{{- \alpha_{2}}\Delta T_{C}} + {\gamma_{1}\Delta H_{R}} - {\gamma_{2}\left( {T_{C} - T_{S}} \right)}}$ where ΔT_(C)=T_(C)−T_(C0) with T_(C0) representing an initial core temperature; T_(C) and T_(S) represent current core and skin temperatures, respectively; dt represents a change in time; ΔH_(R) represents a change in heart rate from an initial heart rate H_(R0); α₂ denotes a thermoregulatory rate constant of T_(C), γ₁ denotes a rate of heat gain due to metabolic activity (H_(R)); and γ₂ represents a rate of heat loss/gain from a core to a skin.
 20. The method according to claim 18, wherein the third equation includes: $\frac{d\Delta T_{S}}{dt} = {{- {\alpha_{3}\left( {T_{S} - T_{A}} \right)}} - {\alpha_{4}\left( {P_{S} - P_{A}} \right)} + {\gamma_{2}\left( {T_{C} - T_{S}} \right)}}$ where ΔT_(S)=T_(S)−T_(S0) with T_(S0) representing initial skin temperature and T_(C) and T_(S) represent current core and skin temperatures, respectively; dt represents a change in time; P_(S) denotes a vapor pressure of water for T_(S); P_(A) represents a vapor pressure of water due to a heat index perceived by humans at a given ambient temperature T_(A) and relative humidity R_(H); γ₂ represents a rate of heat loss/gain from a core to a skin; α₃ represents a rate of convective heat loss/gain from the skin to an environment; and α₄ represents a rate of heat loss to the environment due to sweat evaporation. 